(CBS NEWS) Having cancer appears to protect older people from Alzheimer's disease, according to new research. The study, published July 10 in Neurology, shows the opposite also appears to be true -- having Alzheimer's seems to lower the risk of cancer.
A seemingly no-win scenario to some, the researchers hope their findings could provide more clues to the diseases' protective abilities that can one day be used for medications.
"Since the number of cases of both Alzheimer's disease and cancer increase exponentially as people age, understanding the mechanisms behind this relationship may help us better develop new treatments for both diseases," study author Dr. Massimo Musicco, an Alzheimer's expert at the National Research Council of Italy in Milan, said in a press release.
Researchers looked at a cohort of more than one million residents of Northern Italy. Of those, they included 204,500 older adults aged 60 and over, and tracked them for six years. During that time, roughly 21,500 developed cancer and more than 2,800 developed Alzheimer's disease.
A closer look showed 161 people had both cancer and Alzheimer's disease. However, the researchers calculated based on disease rates among the general population that there should have been 281 people in the Alzheimer's group with cancer, and 246 in the cancer group should have been diagnosed with Alzheimer's.
That indicates a 50 percent drop in cancer risk for Alzheimer's patients and a 35 percent reduction in Alzheimer's risk for older people with cancer.
Mussico noted other studies have found this relationship before, but this is the largest paper to date on the potential link and his research ruled out potential variables, such as people dying from cancer too early to develop Alzheimer's.
One expert noted earlier research showed people with another neurological disorder, Parkinson's, may be less likely to develop cancer.
"I'm hoping this will then convince all the doubters that there is a true inverse association between Alzheimer's, Parkinson's and probably some other neurologic diseases and cancer," Dr. Jane Driver, an assistant professor of medicine who studies aging at Brigham and Women's Hospital in Boston, said to Reuters. She was not involved in the study.
More than 5 million Americans have Alzheimer's or some other form of dementia, and a March report from the Alzheimer's Association found that number is expected to climb to 13.8 million by 2050. That's driven in part by the aging baby boomer population.
About 1,660,290 new cancer cases are expected to be diagnosed this year, according to the American Cancer Society.
Catherine Roe, an Alzheimer's researcher at the Washington University School of Medicine in St. Louis, told USA Today that other scientists laughed at her in 2005 when she published a study linking Alzheimer's with cancer. She said she was excited for the new findings. She wrote an accompanying commentary to the study in the same issue of Neurology.
"It could open avenues of investigation that people haven't even thought of yet," she says. "They've been looking at the usual suspects for so long."
Ryan Jaslow, CBS News